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Two teams of scientists in the US have taken major strides in developing lung tissue that could be used for future transplants or testing the effects of new drugs.

In one study, a team at Yale University in Connecticut implanted engineered lung tissue into rats that worked like the real thing, helping the animals breathe and supplying their blood with fresh oxygen.

In another, a team at Harvard University in Massachusetts developed a tiny lung device from human tissue and synthetic materials to test for environmental toxins or see if new drugs work.

Both studies, published in the journal Science, highlight advances in tissue engineering, in which researchers combine synthetic materials and human cells to work like natural organs.

"This is an early step in the regeneration of entire lungs for larger animals and, eventually, for humans," says Dr Laura Niklason of Yale University.

Starting from scratch

Niklason's team stripped away cells from rat lung that could cause organ rejection, and used the remaining shell as their starting point.

They infused this tissue with lung-specific stem cells and placed them in a bioreactor - a kind of incubator built to resemble foetal-like conditions.

"What we found very much to our surprise was the cells generally landed in their correct anatomical location. We think that means the de-cellularised matrix has (postal) zip codes," says Niklason.

When implanted into rats, the lung functioned much like a normal lung for up to two hours, says Niklason.

At first, "it was pretty close to perfect."

But after a while, blood clots began to form, suggesting some of the cells that coat the blood vessels were sticky.

Niklason says they plan to refine the process.

Lung device

The team led by Donald Ingber, director of Harvard's Wyss Institute for Biologically Inspired Engineering, took an entirely different approach.

The idea was to develop a new way to study the lung that would be useful in drug development and might serve as a replacement for animal studies.

The device, about the size of a pea, mimics the function of air sacs called alveoli, which transfer oxygen through a thin membrane from the lung to the blood.

The device has three parts - lung cells, a permeable membrane and tiny blood vessel or capillary cells. The whole thing is mounted on a microchip.

In one test, the team put E. Coli bacteria on the lung side of the device, and sent white blood cells through the blood vessel side to mimic an immune system response.

The white blood cells invaded the air sac chamber and destroyed the bacteria, says Ingber.

The Harvard team has yet to show the device can actually exchange gases - the essential function of the lung. But they are working on it.

The team at Yale hopes to develop organs made from a person's own cells using embryonic-like stem cells called induced pluripotent stem cells or iPS cells.

"Ultimately, I would love to be able to generate a lung that could be implanted so we don't have to do lung transplants," says Niklason.